1. Field of the Invention
The present invention relates to a method of controlling the output of a fuel cell system including a fuel cell and a load, as well as to a vehicle incorporating such a fuel cell system therein. More particularly, the present invention concerns a method of controlling the output of a fuel cell system in order to effectively utilize the output of the fuel cell, while at the same time suppressing deterioration of the fuel cell.
2. Description of the Related Art
In recent years, intensive efforts have been made to carry out research and development on fuel cells. One of the themes of such research and development is how to control the output of a fuel cell. There have been developed technologies for controlling fuel cell output (see, for example, Japanese Laid-Open Patent Publication No. 06-243882, Japanese Laid-Open Patent Publication No. 2006-202695, and U.S. Patent Application Publication No. 2007/0179636).
According to Japanese Laid-Open Patent Publication No. 06-243882, when the voltage of a fuel cell becomes lower than a threshold value, the fuel cell is turned off in order to prevent deterioration of the fuel cell (see, for example, the summary section of the publication).
According to Japanese Laid-Open Patent Publication No. 2006-202695, in order to cancel a limitation on the output of a fuel cell (20) without adversely affecting the driving performance of a vehicle on which the fuel cell is mounted, the limitation on the output is canceled only when an electric power amount that can be output from the fuel cell while output of the fuel cell is limited exceeds the electric power amount which the fuel cell is required to produce (see, for example, the summary section of the publication).
According to U.S. Patent Application Publication No. 2007/0179636, an output limit (Wout) of a fuel cell (30) is set for purposes of protecting the fuel cell, and output of the fuel cell is limited based on the output limit (Wout) (see, for example, paragraphs [0003] and [0029]). The output limit (Wout) is calculated based on fuel cell temperature (Tfc), inter-cell voltage (Vcel), fuel cell inter-terminal voltage (Vfc), fuel cell electric current (Ifc), and air compressor temperature (Tac) (see, for example, paragraph [0029]).
However, according to Japanese Laid-Open Patent Publication No. 06-243882, Japanese Laid-Open Patent Publication No. 2006-202695, and U.S. Patent Application Publication No. 2007/0179636, sufficient attempts have not been made to suppress deterioration of the fuel cell, and to effectively utilize the output of the fuel cell.